This invention relates to seismic exploration and more particularly to marine exploration. In marine exploration, seismic energy is generated in the water and reflections and refractions of such energy from subsurface formations are detected by a linear string of detectors or hydrophones. The seismic energy sources and the hydrophones are towed through the water to an exploration site by means of cables extending from a marine vessel. At the exploration site, the exploration operation may be carried out with the seismic detector cable either continuously moved through the water during seismic energy generation or fixed in position in the water layer or on the water bottom. Reflection and refraction signals received by the hydrophones along the detector cable are transferred to the marine vessel through the cable wiring for recording and processing.
During the processing of such seismic signals, precise measurements of the hydrophones are required in order to insure maximum accuracy in the static and dynamic corrections generally applied to the obtained seismic data. One method for determining the instantaneous position of various points along a seismic detector cable is disclosed in U.S. Pat. No. 3,953,827 to Le Moal et al and U.S. Pat. No. 4,231,111 to W. P. Neeley. The position of each selected point is determined by measuring the angle of the tangents of the cable at such points with a fixed and known direction, such as magnetic north. At each measuring point along the cable there is located preferably a magnetic compass. By knowing the heading of the tangents to the cable at such plurality of points along the cable and the distances between each of such points, the location of the cable along its entire length can be estimated.
Other systems are known for locating single objects in large bodies of water utilizing the measurement of the time interval required for an energy pulse to travel underwater between two points. One such system is described in U.S. Pat. No. 3,353,149 to D. H. Frantz, Jr., et al.